The present invention relates generally to computed tomography imaging and, more particularly, to a method and apparatus of cardiac CT imaging using ECG and mechanical motion signals.
The narrowing or constriction of vessels carrying blood to the heart is a well-known cause of heart attacks and, gone untreated, can lead to sudden death. In such stenotic vessels, it is known that the region immediately downstream from the constriction is characterized by having rapid flow velocities and/or complex flow patterns. In general, narrowing of blood carrying vessels supplying an organ will ultimately lead to compromised function of the organ in question, at best, and organ failure, at worst. Quantitative flow data can readily aid in the diagnosis and management of patients and also help in the basic understanding of disease processes. There are many techniques available for the measurement of blood flow, including imaging based methods using radiographic imaging of contrast agents, both in projection and computed tomography (CT), ultrasound, and nuclear medicine techniques. Radiographic and nuclear medicine techniques often require the use of ionizing radiation and/or contrast agents. Some methods involve making assumptions about the flow characteristics which may not necessarily be true in vivo or require knowledge about the cross-sectional area of the vessel or the flow direction.
CT is one technique of acquiring blood flow and other cardiac data. Typically, in CT imaging systems, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage, for example. Hereinafter, reference to a xe2x80x9csubjectxe2x80x9d shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam of radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom.
Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to a data processing system for subsequent image reconstruction by an image reconstructor.
A number of methods have been developed for reconstructing cardiac images. One method incorporates prospective electrocardiogram (ECG) gating with axial slice CT acquisition to reconstruct cardiac images. Another method implements a retrospective ECG-gated CT data acquisition and reconstruction technique using spiral CT to reconstruct cardiac images. A prospective ECG-gated technique with spiral CT data acquisition for imaging only the diastolic phase of the heart is also known. These methods use the ECG data signals alone to find data corresponding to the diastolic and systolic phases of the heart. Further, these known methods have a limited applicability when a pacemaker is used to electrically pace the cardiac cycle of the heart. Moreover, detection of certain heart abnormalities such as premature ventricular contraction is difficult with these known imaging techniques.
It would therefore be desirable to design a method and apparatus of cardiac CT imaging that utilizes both ECG and mechanical motion gating signals for image reconstruction.
The present invention is directed to a method and apparatus of cardiac CT imaging overcoming the aforementioned drawbacks. The present invention implements ECG signals and mechanical motion signals of a cardiac region of a subject for image reconstruction. The present invention acquires mechanical gatings of the heart by utilizing changes in pressure, sound, or blood flow acceleration within the cardiac region. The mechanical gatings are then used with ECG data to correlate acquired imaging data with phases of the cardiac region.
Therefore, in accordance with one aspect of the present invention, a method of reconstructing a cardiac CT image of a subject includes the steps of acquiring a set of electrocardiogram (ECG) signals of a cardiac region of the subject and acquiring a set of mechanical motion signals of the cardiac region. The method further includes correlating the set of ECG signals and the set of mechanical motion signals for determining cardiac phases of the cardiac region of the subject. The method further includes reconstructing an image of the cardiac region from the imaging data.
In accordance with another aspect of the present invention, a cardiac imaging system comprising a radiation emitting imaging device, an ECG monitor, and a cardiac motion sensor is provided. The radiation emitting imaging device is configured to acquire CT data of a subject and reconstruct an image of the subject. The ECG monitor is configured to acquire cardiac data of the subject and the cardiac motion sensor is configured to acquire cardiac data associated with mechanical motion of a cardiac region of the subject. A computer program is further provided to acquire a set of ECG signals of the cardiac region from the ECG monitor, acquire a set of mechanical motion signals of the cardiac region from the cardiac motion sensor, and acquire a set of imaging data from the imaging device. The computer is programmed to compare the set of ECG signals and the set of mechanical motion signals to determine phases of the cardiac region. The computer is then programmed to reconstruct an image of the cardiac region from the set of imaging data using the phases of the cardiac region determined from the set of ECG signals and the set of mechanical motion signals.
In accordance with yet another aspect of the present invention, a computer readable storage medium having a computer program stored thereon is provided. The computer program represents a set of instructions that when executed by one or more computers causes the one or more computers to receive a set of cardiac motion signals from at least one cardiac motion sensor affixed to a subject and receive a set of ECG signals from at least one ECG sensor. The one or more computers also analyze the set of ECG signals and the set of cardiac motion signals to determine phases of a cardiac region of the subject and receive imaging data from a data acquisition system configured to receive imaging data. An image is then reconstructed of the cardiac region of the subject.
In accordance with yet a further aspect of the present invention, an imaging apparatus is provided and includes means for acquiring a set of ECG signals from a patient. The imaging apparatus further includes means for acquiring a set of mechanical motion signals of a cardiac region of the patient as well as means for acquiring imaging data from the patient. The imaging apparatus further comprises means for correlating the set of ECG signals and the set of mechanical motion signals to determine one or more phases of the cardiac region of the patient and means for reconstructing an image of the patient from the imaging data using the correlated set of ECG signals and the set of mechanical motion signals to associate the imaging data with one or more phases of the cardiac region.
Various other features, subjects and advantages of the present invention will be made apparent from the following detailed description and the drawings.